Project Summary/Abstract The overall goal of this research plan is to improve understanding about mammalian bile acid chemosignaling through the accessory olfactory system (AOS). Bile acids ? well known regulators of fat digestion and metabolism ? also serve as external chemosignals for the AOS. In most mammals, the AOS directly influences brain regions that control anxiety and social behaviors, and understanding this brain pathway is likely to provide insights into mammalian sexual/reproductive drive, social anxiety, and moods. New knowledge about AOS function may be utilized to help control rodent populations, including those that harbor harmful microorganisms. The mechanisms of peripheral bile acid sensation, the mechanisms of bile acid information processing in the brain, and the behavioral impacts of bile acids are currently unknown. The proposed research will combine new calcium imaging techniques with transcriptome analysis to identify the peripheral AOS receptor(s) sensitive to bile acids. Other proposed experiments will investigate network properties in accessory olfactory bulb (AOB), where bile acid and other steroid information is integrated. Finally, behavioral assessment will be coupled to brain-wide immediate early gene mapping to determine the overall impacts of bile acid chemosensation on brain activity and behavior. The proposed research will investigate these topics in order to improve understanding of this important class of mammalian chemosignals. The results of the proposed experiments will ultimately benefit human health by linking mammalian gut physiology to brain function.